The field of the present invention relates to steam devices and method for rethermalizing food products and holding the rethermalized food products at desired temperatures, including cooking and then conditioning the food products prior to use. More particularly, the invention relates to an oven-type device, which utilizes a steam and air mixture to rethermalize the food products.
The rethermalization of foods and the ability to hold the rethermalized foods for periods of time and at temperatures where the foods are ready for consumption is old in the art. For example, if the foods are prepared in final consumption form prior to freezing or where the foods are ready for further processing, e.g. cooking, in a thawed state, larger institutions, such as schools, hospitals and restaurants, use such rethermalization. Time and labor can be saved if the frozen foods can be taken from a freezer and immediately rethermalized without the necessity of subjecting the foods to a slow defrosting step, which could result in bacterial growth.
The low rate of heat transfer in conventional rethermalizers, e.g. hot air ovens, and the limited capacity of microwave ovens make them undesirable for rethermalization of frozen foods. However, as is known, the latent heat of vaporization makes steam a very effective heat transfer medium because of the large amount of thermal energy contained in the steam. As steam condenses on a food product, this thermal energy will be transferred directly to the food product. Steam is, thus, a much more effective heat transfer medium than hot air. However, because low-pressure steam is generated at a temperature of approximately 212xc2x0 F., steam is generally too hot for direct contact with food products and, thus, can cause damage to some food products. Accordingly, rethermalizing with steam has not been satisfactory for most rethermalizing uses.
Applicants have discovered that by continuously mixing air with low pressure steam and circulating the mixture around the food products, with controlled temperatures of the mixture below 212xc2x0 F., fast, but safe rethermalization of food products can result. This steam-air mixture of the present invention can be established to provide any desired condensing temperature or dewpoint and therefore rethermalize the food products with a high heat transfer rate but at a safe temperature below 212xc2x0 F. Preferably, the steam and air are continuously mixed together.
Further, according to the invention, when the rethermalized food products are left in the present rethermalizer, dry, hot air (without steam) is circulated around the rethermalized food products, and the condition and appearance of the food products can be improved by the evaporation of condensed steam remaining on the products, while at the same time the temperature of the food products is maintained, thus making the food products ready for consumption or further processing as the case may be.
As noted above, the thawing and cooking of food products by circulating steam thereover is not now. Examples of devices for thawing, cooking or otherwise treating food products with steam are disclosed in U.S. Pat. Nos. 3,744,474, 4,426,923, 4,700,685 and 5,613,423. However, none of these patents disclose a device for rapidly rethermalizing food products at temperatures below 212xc2x0 F. without the use of some additional device, such as a vacuum pump, to lower the pressure in a cabinet. Also, as noted above, rethermalizing at or above 212xc2x0 F. can damage some food products. In contrast, the present invention has the advantage to condition the food products utilizing dry, hot air, and thus also avoids the necessity of having to physically move the food products from the thermalizing device.
Thus, briefly stated, the present invention provides a device for rethermalizing food products. An oven chamber has side, top and bottom walls in which at least one is provided with a door to provide access into the chamber. Spaced-apart supports on the side walls support trays in the chamber for containing the food products. A steam generator is provided for generating steam. A plenum adjacent one of the walls has inlets and outlets between the plenum and the chamber. A fan in the plenum mixes air with the steam and moves the mixture from the inlets, through the plenum, to the outlets, preferably horizontally, across a top of each tray, and back to the inlets. A controller controls temperatures of the air and steam mixture to temperatures below 212xc2x0 F. to rethermalize the food products, in part, by the steam in the mixture condensing thereon.